Method and device for verifying the operating condition of a system for recovering vapors originating from the fuel tank of a motor vehicle

ABSTRACT

A method and device for verifying the operating condition of a system for recovering vapors from a vehicle fuel tank. A vapor cartridge is insulated from the outside air and the vapor circuit of the recovery system is connected, on the one hand, to the intake port of the engine and, on the other hand, to an outlet line for the exhaust gases from the engine. The device selectively activates insulation and connection valves to sweep the cartridge with exhaust gas. Richness in oxygen of the air-fuel mixture supplied to the engine is then measured and compared with a predetermined value in order to deduce the presence of a break in the vapor circuit when the predetermined value is exceeded.

The present invention relates to a method and a device for verifying theoperating condition of a system for recovering vapours originating froma fuel tank and, more particularly, to such a device designed to beinstalled in a motor vehicle propelled by an internal combustion engine.

When filling the petrol tank of such a vehicle, or when the petrolcontained in this tank is heated up, petrol vapours are released abovethe free surface of the petrol contained in the tank. These vapours arenormally discharged into the open air. However, some antipollution lawsinsist that these vapours are recovered in order to protect theenvironment. In order to conform with these laws, vapour-recoveringsystems have been designed which essentially comprise a cartridge filledwith active carbon, the cartridge being connected to the petrol tank soas to collect the hydrocarbon vapours released therefrom, these vapoursbeing absorbed by the active carbon until the latter is saturated.

In order to avoid having to replace the cartridge when the active carbonis saturated, means for regenerating the active carbon are incorporatedinto the system which operate by sweeping this active carbon with astream of air. Indeed, the active carbon is regenerated under the actionof the oxygen contained in the air which passes through it. In order toeffect this sweeping of the active carbon by a stream of air, thecartridge is connected to the intake port of the internal combustionengine which propels the vehicle, the engine then serving as a suctionpump. The vapours recycled in this way are then combusted in the engine.

A solenoid valve is conventionally installed between the cartridge andthe intake port of the engine. This solenoid valve is controlled byelectronic means such as an ignition and/or injection calculator whichcontrols the engine, this calculator furthermore generating a controlsignal for the solenoid valve which selectively intitiates theconnecting of the cartridge to the intake port of the engine, when it isjudged to be necessary to empty this cartridge.

The solenoid valve, the cartridge, the petrol tank and the intake portare connected by pipes (or "durit", a trade mark) which can becomedetached from the elements to which they are connected as a result ofbeing accidentally pulled off or as a result of the vibrations to whichthe vehicle is subjected, for example. In the event of disconnection,the system for reprocessing petrol vapours becomes, of course,inoperative. The occurrence of such a situation must be detected so thatcorrective measures may be implemented to prevent the environment frombecoming polluted, the petrol vapours otherwise being ejected to theenvironment when a "durit" has been disconnected.

European Patent Application EP-A-0 411 173 describes a tank ventilationsystem whereby deficiencies in the system are detected as promptly aspossible.

This problem is solved by providing a system for the detection ofdefects in a tank ventilation system wherein in a line between an outputof the filter to an intake portion of the internal combustion engine aflow sensor is arranged which supplies a flow signal to the controlunit. A lambda probe may also be provided which supplies a probe signalto the control unit, the lambda probe being provided at an exhaustportion of the internal combustion engine. Means are provided forcomparing the at least one of flow signal from the flow sensor or theprobe signal from the lambda probe to a control signal which actuatesthe tank ventilation valve. An error signal is provided in the case of alogically unreasonable comparison of these signals which is indicativeof a defect in the tank ventilation system.

French Patent Publication No. 2,635,823, published on Mar. 2, 1990,proposes a device for verifying the operating condition of a system forrecovering vapours, comprising means for detecting any possible break inthe circuit that the petrol vapours follow, both during the normalabsorption of the vapours in the cartridge of active carbon and whenthis cartridge is being emptied. These means selectively sense thepressure prevailing in the said vapour circuit, when the cartridge isconnected to the intake port of the engine, in order to indicate afailure of the circuit when the pressure sensed is greater than apredetermined value. Indeed, in the event of an accidental break in thecircuit, the pressure in the latter corresponds to the atmosphericpressure and no longer to the pressure prevailing in the intake port ofthe engine. By then comparing the pressure in the vapour circuit with apredetermined pressure, in other words, atmospheric pressure, it ispossible to detect any break in the vapour circuit, requiringintervention intended to remedy it. According to an advantageousembodiment of the device described in the abovementioned Frenchdocument, the means for sensing the pressure in the vapour circuitconsist of a pressure sensor normally used to supply, to an ignitionand/or injection calculator controlling the operation of the engine, theintake pressure of this engine, an essential parameter for thecalculations carried out by the calculator. A single pressure sensor isthus used for two purposes, in a particularly economical way.

The device described in the abovementioned French document entailsapplying a partial vacuum to the petrol tank, normally equipped with anoverpressure/depressurising valve. In the event of the latter failing,the application of a partial vacuum to the tank is liable to damage thewall of the tank. Furthermore, the use of the sensor for the intakepressure of the engine to measure the pressure in the tank obviouslyprevents, during this latter measurement, the intake pressure from beingsupplied to the ignition and/or injection calculator.

The object of the present invention is thus to provide a method and adevice for verifying the operating condition of a system for recoveringvapours originating from the fuel tank of a motor vehicle, which do nothave the limitations listed above of the device described in theabovementioned French document.

This object of the invention, and others which will become apparent onreading the present description, is achieved with a method for verifyingthe operating condition of a system for recovering vapours originatingfrom the fuel tank of a motor vehicle propelled by an internalcombustion engine, this system comprising a cartridge for recoveringthese vapours by filtering, placed in a vapour circuit connected, on theone hand, to the fuel tank and capable of being connected selectively,on the other hand, to the intake port of the engine. According to theinvention, the cartridge is selectively swept with a stream of gasoriginating from the exhaust of the engine, the intake port of thisengine is supplied with the stream of gas once it has swept thecartridge, the richness in oxygen of the air/fuel mixture which thensupplies the engine is measured, and the presence of a break in thevapour circuit is deduced from any exceeding of a predetermined value bythe measured richness in oxygen.

Thus, when testing the integrity of the vapour circuit, the engine drawsexhaust gases through this circuit. Since the exhaust gases are weak inoxygen, the air entering into the engine is itself weakened in oxygen.Confirmation of this weakening by measuring the richness in oxygen ofthe air/fuel mixture supplying the engine is then indicative of the factthat no entry of parasitic air, with a normal richness in oxygen, isaffecting the vapour circuit.

In order to implement this method, the invention provides a devicecomprising (a) means for insulating the cartridge from the outside airand for connecting the vapour circuit of the recovering system, on theone hand, to the intake port of the engine and, on the other hand, to anoutlet line for the exhaust gases from the engine so as to sweep atleast the cartridge with these gases under the effect of the suctiondeveloped in the intake port of the engine, (b) means for selectivelyactivating these insulation and connection means, (c) means for thenmeasuring the richness in oxygen of the air/fuel mixture supplying theengine and (d) means for comparing the measured richness with apredetermined value in order to deduce the presence of a break in thevapour circuit from any exceeding of this predetermined value by themeasured richness in oxygen.

Other features and advantages of the method and of the device accordingto the invention will become apparent on reading the description whichfollows and on examining the attached drawing, in which:

FIG. 1 is a diagrammatic representation of a first embodiment of thedevice according to the invention, and

FIG. 2 is a diagrammatic representation of a second embodiment of thedevice according to the invention.

Reference is made to FIG. 1 of the attached drawing, in which is can beseen that the device according to the invention comprisesconventionally, a cartridge 1 for recovering petrol vapour, arranged ina vapour circuit connecting the cartridge 1, on the one hand, to apetrol tank 2 via a duct 3 and, on the other hand, to the intake port 4of an internal combustion engine via a duct 3'. The intake port 4 of theengine is conventionally equipped with an air filter 5 and with abutterfly valve 6 for regulating the quantity of air entering into theengine. Connection means consisting of a two-orifice and two-positionshut-off solenoid valve 7 are arranged in the duct 3' in order to makeit possible to control selectively the connection of the cartridge 1 tothe intake port 4, as is well known. As is also well known, thecartridge 1 comprises an air inlet 8 that permits sweeping of thecartridge by a stream of air from outside under the effect of a suctiondeveloped by the intake port of the engine, during the emptying of thecartridge. According to the invention, insulation means consisting of atwo-orifice and two-position solenoid valve 9 are mounted on this airinlet in order to permit the selective control of the opening and theclosing of this air inlet. The solenoid valves 7 and 9 are controlled bya calculator 10 on board the vehicle and furthermore comprising, forexample, means for controlling ignition and/or for regulating theair/fuel mixture supplying the engine.

According to an essential feature of the device according to theinvention, it comprises means for connecting selectively the vapourcircuit of the system for recovering petrol vapours described above toan outlet line 11 for the exhaust gases from the engine, which canconventionally comprise a catalytic convertor 12 and a silencer 13placed in series in the line 11. These connection means can consist of aduct 14 joining the line 11, between the catalytic convertor 12 and thesilencer 13, to the space 15 situated above the free surface of thepetrol 16 contained in the tank 2. A two-orifice and two-positionsolenoid valve 17 is placed in the duct 14, this solenoid valve beingcontrolled by the calculator 10.

Also according to the invention, the device comprises means formeasuring the richness in oxygen of the air/fuel mixture supplying theengine. When this is controlled by a device for the closed-loopregulation of the air/fuel mixture, such measurement means are normallyincorporated into this device and then take the form of an oxygen probe18 placed in the exhaust line 11 as is well known in practice. The probe18 then provides a signal to the calculator 10 which controls theregulation device. In order to verify the operating condition of thesystem for recovering vapours, and in particular the lack of any breakin the vapour circuit, in the region of the connections of the duct 3 tothe tank and to the cartridge, and of the duct 3' to the same cartridgeand to the intake port of the engine, or between these connections, theopening of the solenoid valves 7 and 17 and the closing of the solenoidvalve 9 controlling the air inlet of the cartridge 1 are controlled viathe calculator 10. The suction thus developed by the intake port 4 ofthe engine in the tank 2 via the ducts 3 and 3' causes the free space 15in this tank to be filled with exhaust gases drawn off through the duct14 from the line 11. These exhaust gases, lean in oxygen, sweep thecartridge 1 before being incorporated, via the duct 3', into the airentering into the engine under the control of the butterfly valve 6. Thelowered oxygen content of the air/fuel mixture which then supplies theengine is detected by the oxygen probe 18 which sends to the calculatora signal which is representative of this lowered oxygen content. Thecalculator comprises means (not shown) for comparing the richness inoxygen of the exhaust gases, which richness is measured by the probe 18,with a predetermined threshold value. When the measured richness fallsbelow this predetermined value, it can be concluded that the vapourcircuit has: not been affected by any entry of parasitic air and that,consequently, the system for recovering vapours is functioningcorrectly.

If, on the other hand, the richness in oxygen measured by the probe 18is greater than this threshold, it must be concluded that the expecteddecreased richness of the air/fuel mixture in oxygen has been disturbedby the entry of quantities of parasitic air which has enriched therecycled exhaust gases in the intake port 4 of the engine with oxygen.The entry of quantities of parasitic air in this way normally results,as we have seen above, from disconnections of the ducts 3 and 3' whichcan become detached from the members to which they are connected as aresult of accidentally being pulled off or of vibrations to which thevehicle is subjected, for example. This entry of quantities of air canalso result from the ducts 3 and 3' becoming pierced or rupturing, forexample owing to aging. In such an eventuality, the calculator excites avisual or sound alarm member, for example, which signals that the systemfor recovering petrol vapours must be checked urgently with a view tomaking good the faulty connections or to replacing the pierced or cutducts.

It is known that the petrol tank 2 can be equipped with anoverpressure/depressurising valve which approximately regulates thevapour pressure prevailing in the tank. In an alternative version of thedevice illustrated in FIG. 1, the duct 14 could be connected to the tank2 by such an overpressure/depressurising valve 19 (showndiagrammatically in broken lines).

When testing the system for recovering vapours, the device for verifyingthe operating condition of this system illustrated in FIG. 1 is assigneda certain time constant owing to the fact that the air/fuel mixtureentering into the engine only becomes lean in oxygen after the freespace 15 of the tank has been emptied and this space has been filledwith exhaust gases.

This disadvantage is avoided with the device illustrated in FIG. 2,where reference numerals identical to references used in the device inFIG. 1 refer to identical or similar elements or members. In thisfigure, it is immediately apparent that the air inlet 8 of the cartridge1 can be connected selectively to the outlet line 11 for the exhaustgases by a duct 20, the connection being controlled by a two-way andtwo-position solenoid valve 21, this solenoid valve being controlled bythe calculator 10 in the same way as the "emptying" solenoid valve 7. Inthe position illustrated in FIG. 2, the solenoid valve 21 connects theair inlet 8 to the outside air, whereas, in its other position, itconnects this air inlet 8 to the duct 20. In this latter position, usedwhen testing the vapour circuit, the suction developed by the intakeport of the engine causes a stream of exhaust gas, lean in oxygen, topass through the cartridge 1 before recycling this stream into theintake port of the engine. This circulation makes it possible to verifythat no air has entered either into the duct 3' or into the duct 3.Indeed, if, despite this duct 3 and the tank 2 not being filled by theexhaust gases drawn through the cartridge 1, parasitic air enters in theregion of the duct 3, this parasitic air which has entered is itselfdrawn in by the intake port through the cartridge and the duct 3'. Theoxygen probe 18 does not then detect the decrease in oxygen contentwhich is representative of the lack of any air having entered the vapourcircuit.

It may be noted in passing that, in the device in FIG. 2, use is made ofthe control of only two solenoid valves instead of the three solenoidvalves used in the device in FIG. 1.

The invention is not, of course, limited to the embodiments describedand illustrated which have been given purely by way of example. Theinvention can thus be applied to any vehicle equipped with an oxygenprobe, whether this vehicle is equipped with a catalytic convertor ornot.

What is claimed is:
 1. A method for verifying an operating condition ofa system for recovering vapors originating from a fuel tank of a motorvehicle propelled by an internal combustion engine, wherein the systemincludes a vapor circuit, a filter cartridge for recovering the vapours,the filter cartridge being connected in the vapor circuit andcommunicating with the fuel tank, and a sensor for measuring a richnessin oxygen in an exhaust gas of the engine, the method whichcomprises:selectively connecting the filter cartridge to an intake portof the engine; sweeping a stream of exhaust gas from the engine throughthe filter cartridge and supplying the stream of gas from the filtercartridge to the intake port; detecting a richness in oxygen of anair/fuel mixture supplying the engine; and deducing that a break existsin the vapor circuit if the richness in oxygen detected by the sensorexceeds a predetermined threshold value.
 2. In a recovering system forrecovering vapors originating from a fuel tank of a motor vehiclepropelled by an internal combustion engine, wherein the recoveringsystem includes a vapor circuit, and a filter cartridge for recoveringthe vapors, the filter cartridge being connected in the vapor circuitand communicating with the fuel tank, a device for verifying anoperating condition of the recovering system, comprising:sensor meansfor measuring a richness in oxygen of an exhaust gas of the engine;means for selectively connecting the filter cartridge to an intake portof the engine; means for comparing a measured richness in oxygenmeasured by said sensor means with a predetermined value and fordeducing that a break exists in the vapor circuit if the measured valueexceeds the predetermined value; means for isolating the filtercartridge from air outside the vapor circuit, communication means forconnecting said vapor circuit to an exhaust gas outlet line for theexhaust gas from the engine and for sweeping said cartridge with theexhaust gas under an effect of a suction developed in the intake port ofthe engine, and activating means for selectively activating saidisolating means.
 3. The device according to claim 2, wherein the vehiclehas means for closed-loop regulation of an air/fuel mixture supplyingthe engine, and wherein said sensor means for measuring the richness inoxygen of the air/fuel mixture include an oxygen probe forming a part ofthe closed-loop regulation means.
 4. The device according to claim 2,wherein said filter cartridge has an air inlet opening, saidcommunication means including a duct joining the exhaust gas outlet lineto said air inlet opening and valve means for selectively connectingsaid duct to said air inlet and isolating said filter cartridge fromoutside air.
 5. The device according to claim 4, wherein said activatingmeans are a calculator receiving signals from said sensor means, saidvalve means being in the form of a solenoid valve controlled by saidcalculator.
 6. The device according to claim 2, wherein the vehicle hasa fuel tank with an inner free space defined above a fuel level in thefuel tank, said communication means including a duct joining the exhaustgas outlet line to the inner free space for filling said inner freespace and said vapor circuit with exhaust gas under a suction developedin the intake port of the engine.
 7. The device according to claim 6,including a solenoid valve for selectively connecting the fuel tank tothe exhaust gas outlet line.
 8. The device according to claim 6,including an overpressure/depressurizing valve connected in said ductbetween the fuel tank and the exhaust gas outlet line.
 9. The deviceaccording to claim 7, including an overpressure/depressurizing valveconnected in said duct between the fuel tank and said solenoid valve.